The aim of the proposed research is the further elucidation of the functional organization of the vertebrate spinal cord, utilizing electrophysiological techniques. The main thrust of our research effort at present is in the identification of specific categories of spinal cord neurons and in the study of their response characteristics. The experiments currently planned will be upon the cells of origin of the spinothalamic tract in the monkey. A quantitative study of the responses of these cells to controlled mechanical and thermal stimulation will be the main effort. Both excitatory and inhibitory receptive fields will be examined, and an effort will be made to identify the types of sensory receptors responsible for modifying the activity of these cells.